The present invention relates to the diagnostic imaging arts. It particularly relates to helical volumetric computed tomography (CT) imaging employing a geometric configuration in which the gantry is tilted relative to its axis of rotation, and will be described with particular reference thereto. However, the invention will also find application in other types of tomographic volumetric imaging using tilted geometric configurations.
Computed tomography (CT) imaging employs a radiation source, typically an x-ray source, that generates a fan-beam or cone-beam of x-rays that traverse an examination region. A subject arranged in the examination region interacts with and absorbs a portion of the traversing x-rays. In volume imaging, a two-dimensional detector array is arranged opposite the x-ray source to detect and measure intensities of the transmitted x-rays. Typically, the x-ray source and the detector array are mounted at opposite sides of a rotating gantry and rotate together as the gantry is rotated to acquire data over an angular range of projection views.
In helical CT imaging, the subject is advanced linearly through the examination region along a direction that is perpendicular to the gantry rotation plane such that the x-ray source traverses a helical trajectory relative to the subject. X-ray absorption data acquired during the helical orbiting is reconstructed using any of several known three-dimensional reconstruction methods such as an approximate n-PI filtered backprojection reconstruction method, an exact n-PI reconstruction method, or the like. The selected reconstruction generates a three-dimensional image representation of the subject or of a selected portion thereof.
In certain medical diagnostic applications of helical CT imaging, it is desirable to use a tilted gantry geometry in which the gantry rotation plane is tilted respective to the linear patient advancement direction. For example, in imaging of the head a substantial gantry tilt of up to 30xc2x0 beneficially reduces radiation exposure of radiation-sensitive eye tissues. For imaging curvilinear anatomical structures such as the spine the gantry is beneficially dynamically tilted during imaging to keep the scanned structure generally perpendicular to the rotating gantry.
A problem arises because the tilted geometry results in a sheared helical trajectory of the x-ray source. The shearing is not accounted for in conventional helical computed tomography reconstruction techniques, and leads to substantial image degradation.
The present invention contemplates an improved apparatus and method that overcomes the aforementioned limitations and others.
According to one aspect of the invention, an apparatus is disclosed for generating an image representation of an imaged subject from volumetric helical computed tomography imaging data acquired using a tilted gantry geometry. A means is provided for transforming the imaging data to a zero tilt geometry. A means is provided for rebinning the transformed imaging data to a non-sheared detector window. A means is provided for reconstructing the transformed and rebinned imaging data to generate a three-dimensional image representation.
According to another aspect of the invention, a method is provided for generating an image representation of an imaged subject from volumetric helical computed tomography imaging data acquired using a tilted gantry geometry. The imaging data is transformed to a zero tilt geometry. The transformed imaging data is rebinned to a non-sheared detector window. The transformed and rebinned imaging data is reconstructed to generate a three-dimensional image representation.
According to yet another aspect of the invention, an apparatus is disclosed for performing volumetric helical computed tomography imaging of a subject. A computed tomography scanner acquires helical computed tomography imaging data using a tilted gantry geometry. In the tilted gantry geometry, a rotational plane of a rotating radiation source is tilted with respect to a direction of linear motion of the subject. A transform processor transforms the imaging data to a zero tilt geometry. A rebinning processor rebins the transformed imaging data to a non-sheared detector window. A reconstruction processor reconstructs the transformed and rebinned imaging data to generate a three-dimensional image representation.
One advantage of the present invention resides in simplified reconstruction of computed tomography imaging data acquired using a tilted gantry configuration.
Another advantage of the present invention resides in transforming tilted gantry computed tomography imaging data to a zero tilt geometry which is readily reconstructed by any of a variety of reconstruction techniques.
Numerous additional advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment.